The present invention relates to a double belt conveyor for the continuous production of laminates having a foam core foamed in situ between covering layers, from a flowable reaction mixture, comprising a lower endless slat belt and an upper endless slat belt, which belts are provided with guiding devices, the slat belts forming the boundary of a foaming area between them, having a common drive and rotating at the same speed.
Double belt conveyors of the type described above have been constructed in such a way that the slat belts are driven via deflecting wheels positioned at the discharge end of the conveyor. For the purpose of synchronous running, the upper slat belt is driven by a cardan drive which is coupled to the drive of the lower slat belt, or by an equivalent non-slip power transmission. The individual slats of the slat belts cannot be made as narrow as one would wish due to cost and stability. A so-called "polygon effect" is thus produced due to the polygon-like design of the deflecting wheels. This results in the slat belts travelling at a pulsating speed. This effect becomes even greater as the width of the slats increases. Additionally, there is a periodic rise and fall of the individual slats.
Various attempts have been made to eliminate or reduce the polygon effect.
The possibility of increasing the diameter of the deflecting wheels cannot be considered due to the greater (and in most cases unacceptable), structural height of the double belt conveyor which would result. The alternative possibility of providing narrower slats has also been rejected for reasons which have been mentioned above.
A proposal has been made (German Offenlegungsschrift 3,018,357) to eliminate the polygon effect by electric, means. To achieve this, considerable investment in transmitters and electrical control circuits having desired/actual value comparison is necessary.
According to a further proposal (German Pat. No. 3,031,130) a deflecting wheel for a slat belt is firmly connected to a polygon-chain wheel having the same number of corners, which chain wheel is driven by a fine toothed chain with a uniform speed of rotation. By appropriately staggering the corners of the two wheels with respect to each other, the polygon effect is partially compensated.
Although both measures allow the fluctuations in speed to be reduced, they do not adequately prevent the rise and fall of the slats.
Finally, a further proposal is based on extending the running rails for the slat belts into the moving or rotating region of the deflecting chain wheels, thereby ensuring that the running rails also provide guidance in the transitional area. This prevents the rise and fall of the slats but not the polygon effect itself.
The object of the present invention is to eliminate the polygon effect or to reduce the effects thereof in such a way that both the pulsating speed of the slat belts and the rise and fall of the slats are prevented to as large an extent as possible.